1. Field of the Invention
The present invention relates to an electronic scanning ultrasonic diagnostic system and more particularly to an electronic scanning ultrasonic diagnostic system which emits sector scanning ultrasonic beams.
2. Prior Art
It is well known to observe a human body for medical treatment by ultrasonic diagnostic equipment which emits ultrasonic beams into the human body to be examined and receives echoes reflected from tissues in the body. Scanning of the ultrasonic beam along the desired section can display B-scope image and provide various diagnosis information promptly. As for the scanning method of the above mentioned ultrasonic beams, there is a method of manual or mechanical handling of a probe which emits ultrasonic beams, and there is another way of high speed scanning method in which the probe is fixed and ultrasonic transducers arranged in a row in the probe is electronically controlled. The latter electronic scanning type probe are widely utilized, since it acts rapidly and allows real-time images of dynamic tissue motion to be observed. The electronic scanning type probe is ordinarily classified into linear scanning method and a sector scanning method. In order to observe internal tissues which occupy relatively most of the body, preferred is the sector scanning method in the latter. In the case observing a heart in motion at real-time particularly, it requires 10 cm in effective observing length, and preferred is the probe in the sector scanning method which provides sector ultrasonic beams emitted from small ultrasonic beam emitting surface in wide emitting angle, since utilization of the probe in such length in the conventional linear scanning method hardly produces clear tomograms, being affected by images of ribs or the like.
In FIG. 1, shown therein is a conventional sector electronic scanning type probe. The probe 12 attached to a human body 10 emits ultrasonic beams 200 into the body 10 at a predetermined emitting angle 100. According to the sector electronic scanning type probe described in FIG. 1, the ultrasonic beams 200 can be emitted towards the heart between the adjacent ribs and can display a considerably wide area of the tissue producing a clear image, accordingly.
In the prior art device in FIG. 1, however, there are such drawbacks that the circuit composition is extremely complicated for the achievement of accurate delay control at the plural ultrasonic wave transducers built in the probe 12 at every timing of emitting and receiving the ultrasonic waves in order to obtain the sector scanning ultrasonic beams 200. In the conventional electronic scanning probe, there exists interference among ultrasonic wave signals emitted from each of the ultrasonic wave transducers having respective different delay times, and unnecessary artificial echoes having different directivities are produced. The ultrasonic wave transducers must be arranged in a row at shorter distances or the exciting frequency of the ultrasonic waves must be lowered so that the unnecessary artificial echoes can be less produced, which is another drawback limiting the resolution of reflected echoes. Furthermore, in the prior art device illustrated in FIG. 1, in the vicinity of the beam emitting surface there exists an area 300 drawn with oblique lines which is unable to be observed since the origin of the coordinate axis of the emitting angle 100 is determined in the center of the beam emitting surface of probe 12.
For the other improved conventional sector electronic scanning type probe, a concave probe is introduced as shown in FIG. 2. This prior art device can provide the sector ultrasonic beams 200 by means of simple control circuit without supplying respectively different delay times to each of the ultrasonic wave transducers as described in FIG. 1, since the ultrasonic waves transducers are concavely arranged at equal distances. In the prior art device, however, a concave beam emitting surface 12a of the probe 12 does not contact the surface of the body 10 to inevitably make a gap between the both, which causes the remarkable attentuation of the ultrasonic beams, and a contact spacer 14 consisting of medium well passing ultrasonic waves must be installed on the beam emitting surface 12a as illustrated in FIG. 2. The contact spacer 14 has an advantage that an intersection 200a of ultrasonic beams 200 can be established in the vicinity of the surface of the body 10 as well as the gap between the beam emitting surface 12a of probe 12 and the surface of the body is buried. However, in this prior art device, the particular contact spacer makes the equipment complicated and less operational. Furthermore, the contact spacer 14 shown in FIG. 2 causes drawbacks such that there exists the attenuation of ultrasonic waves in its inside and the attenuating action decreases the echoe receiving sensitivity.